As a technique for producing foamed articles of elastomer (vulcanized rubber), a process has hitherto been known, in which a vulcanizing agent and a foaming agent are admixed to natural rubber or a synthetic rubber and kneaded, whereupon the resulting kneaded mass is formed into a contemplated shape, followed by heating to effect vulcanization and foaming to obtain a foamed article of elastomer.
By the above-mentioned prior technique, however, it is necessary for forming the said rubber into a predetermined shape by continuous extrusion to perform preliminarily a process step of kneading a composite blend together with the rubber to obtain the kneaded mass before the continuous extrusion and to carry out thereafter a process step of forming the kneaded mass into a form of ribbon preliminarily for facilitation of easy supply of the kneaded mass to the extruding machine before the continuous kneading. Thus, the prior technique as given above is disadvantageous in the industrial production, since the production process steps are intricate and, in addition, considerable time is required for both the process steps of vulcanization and of foaming.
As a technique for solving such problems, there is a method of using, for example, a thermoplastic resin, such as an ethylene/vinyl acetate copolymer, low density polyethylene or so on, or a partially cross-linked thermoplastic elastomer constituted of an olefinic copolymer rubber and an olefinic resin. According to this method, the process steps mentioned above can be dispensed with.
However, thermoplastic resins and thermoplastic elastomers conventionally used have problems that inferior appearance may be apt to occur due to the tendency to occurrence of defoaming upon the foaming molding and that the foaming expansion ratio of the foamed article is lower, as amounting only to about 1.5 times, whereby a harder hand touch will result.
Further, when a part element subject to repeated sliding or a partial component subject to contact with human or materials, such as weather strip or sealing element on window sash for automobile, is produced from a conventional foamed body, it may difficultly be served for practical use as a sliding element or the like by inferior durability thereof due to the poor resistance to abrasion and lower sliding performance thereof.
An object of the present invention is to solve the problems concomitant with the prior technique mentioned above and to provide a foamed laminate based on olefin which is made of an olefinic polymer premitting recycled use and obtainable at a high foaming expansion ratio and, thus, exhibits a soft hand touch and which is superior in the appearance, in the resistance to abrasion, in the durability and in the sliding performance, in particular, is superior in the resistance to abrasion under a difficult condition.
Another object of the present invention is to provide a sliding element, an automotive weather strip and a sealing element for architectural use, made of the above-mentioned foamed laminate based on olefin.